Mac下安装Python2和Python3共存

  一般是python2默认安装了，python3没有安装，这时候一般使用命令：brew install python3 进行安装
  这里有个基础知识要记录一下，就是不同方法安装python的路径是不一样的，如下所示：

来源	Python安装路径
系统安装路径	/System/Library/Frameworks/Python.framework/Versions/2.7
brew安装	/usr/local/Cellar/python
官网PKG安装	/Library/Frameworks/Python.framework/Versions/2.7

1. 控制台输入：vim ~/.bash_profile 并输入如下代码：

   # Setting PATH for Python 2.7
   PATH="/System/Library/Frameworks/Python.framework/Versions/2.7/bin:${PATH}"
   export PATH
   # Setting PATH for Python 3.7.3
   PATH="/usr/local/Cellar/python/3.7.3/bin:${PATH}"

2. 控制台输入：vim ~/.bashrc 完成别名的命名

   alias python2='/System/Library/Frameworks/Python.framework/Versions/2.7/bin/python2.7'
   alias python3='/usr/local/Cellar/python/3.7.3/bin/python3.7'
   alias python=python3

3. 需要source一下

   source ~/.bash_profile
   source ~/.bashrc